Taksy - Have you run into Susano and the bear yet? It sounds like you are having trouble learning the bloom brush technique?

If you are in the inner Hana Valley, at the very end you'll come to an area with a small guardian sapling. To the left is a gated passageway. Use the brush to slash the gate then enter. It winds around to a dead end where Susano and the bear are. Help Susano slash the torches and the bear will drop a round crystal ball. Roll it out to where the sapling is and place it on the pedestal. Now you can paint the sun into the sky and it will reveal a constellation. From it you will get the bloom technique and that will enable you to bloom the sapling in Shinshu to removed the cursed zones.

On your way out of Hana, don't forget to use the new bloom technique to revive all the dead trees. If you get them all, a new treasure (a sun disc fragment) will appear at the mural inside the cave!

If this is where you are stuck, let me know if this helped. If not, we'll figure something else out for you!